This invention relates broadly to high-energy oxidizers for solid, rocket propellants. More specifically, it relates to the preparation and use in propellants of cocrystals of cyclotetramethylenetetranitramine (HMX) and ammonium perchlorate.
The currently most widely used type of solid, rocket propellant comprises essentially a dispersion of finely divided inorganic oxidizer particles together with a powdered, metallic fuel, in an elastomeric binder. Such propellants are commonly made by mixing a major amount of the finely divided oxidizer with powdered metal and a minor amount of liquid, curable organic polymer, a curing agent for the organic polymer, and small amounts of certain special purpose additives. The resulting mixture is usually heated to an elevated temperature to cure the polymer to elastomeric form with the oxidizer dispersed therethrough.
The thrust that a given rocket structure develops depends importantly on the specific impulse of the propellant used therein, and the specific impulse in turn depends importantly on the nature of the oxidizer employed.
Although ammonium perchlorate has been probably the most successful and widely used oxidizer for solid rocket propellants, its high degree of solubility in water tends to affect aging properties of solid propellant adversely, primarily by the formation of perchloric acid from the ammonium perchlorate and ambient moisture. This necessitates the use of desiccants and hermetic seals with such rocket motors, especially in humid climates. Such undesirable products that may also be formed with residual moisture in the propellant can attack the aluminum powder, that is a common ingredient of propellant, to cause gassing and a resultant production of voids in the propellant. Such unplanned voids can greatly increase the burning surface of the propellant, and, hence, its burning rate, to an undesirable extent.
Cocrystals of ammonium perchlorate with burning-rate depressants have been described in the prior art literature as having been successfully used in solid propellant; but these also have been water soluble, and, hence, have done nothing to solve the problems associated with such water solubility in solid propellant.